In the fabrication of semiconductor memory devices and other types of integrated circuits, two or more conductive layers known as interconnect layers are commonly deposited. These interconnect layers are separated, for example, by one or more dielectric layers. Various methods may be used to make electrical connections between these interconnect layers. One such method includes (a) forming a first dielectric layer, (b) depositing a first interconnect layer ("Poly 1"), (c) masking and etching Poly 1 to form conductive leads, (d) depositing a second dielectric layer, (e) masking and etching the second dielectric layer to form a "via" (a small opening) completely through the second dielectric layer to a Poly 1 conductive lead, and (f) depositing a second interconnect layer ("Poly 2") in and over the via so that electrical contact between Poly 1 and Poly 2 is made through a "plug" of conductive material which fills the via. One of the difficulties in using this method is that it is necessary to compensate for possible misalignment of the via mask. For example, a misalignment of the via mask may shift the via sideways so that the via is not formed entirely over the Poly 1 conductor. Instead, the via may overlap onto the first dielectric layer alongside a Poly 1 conductor, exposing the first dielectric layer during the via etch step, and allowing a groove to be etched in the first dielectric layer during the via etch step. The groove may cause microcracking or thinning of the Poly 2 conductor when it is deposited in and over the via to contact the Poly 1 conductor. This can be avoided by widening the Poly 1 conductor at the via location so that even a misaligned via will not overlap onto the first dielectric layer. However, locally widening the Poly 1 conductor conflicts with the goal of reducing the size of the integrated circuit and increasing its packing density.
It is desirable to decrease the memory cell size in fabricating semiconductor memory devices such as random access memory chips, in order to increase the packing density. A major factor limiting further increases in packing density is the alignment tolerance of the via mask used in forming a via between Poly 1 and Poly 2.